1. Field of the Invention
The present invention relates to the machining of airfoil blades for gas turbine engines.
2. Description of the Prior Art
The complex shape of airfoils, such as gas turbine engine rotor blades, is a characteristic that impede economical methods of milling. The normal manner to produce this complex shape is a technology using the point milling method. According to the point milling method, a ball end mill is used to machine an airfoil. The tool path is programmed such that the tool's ball nose creates the part profile point by point. This method uses a limited portion of the cutter and is time consuming. The relatively poor productivity is explained by the fact that it takes a huge number of passes for the tool to cover all the airfoil surface points. In addition, the tool has a relatively poor rigidity, which limits the tool load.
In order to minimize the number of tool passes, flank milling was developed for airfoil machining. In flank milling, a taper ball end mill is used. The tool path is programmed such that the tool has a curved contact surface with the airfoil. The whole surface of the airfoil is produced by one single tool pass, increasing considerably the productivity with respect to the point milling method. The tool (a taper ball end mill) is characterized by a small diameter and a long flute length. Because of the part being milled, the tool shank is very long as well. All this results in reduced tool rigidity. The poor tool rigidity and the long axial tool immersion, limit the tool load. This results in a relatively poor metal removal rate, which is not suitable especially for the roughing operations.
To improve productivity, there is thus a need for a new airfoil machining method which allows the use of a stronger tool and a higher chip load.